It is postulated that pathological changes in vessel structure seen in conditions such as hypertensive arteriopathy are induced in part by signaling pathways that govern cell growth, death, differentiation and matrix production. Within the spectrum of identified arteriopathies, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), is a heritable syndrome of systemic small vessel disease predisposing to stroke and vascular dementia. The pathological changes defined in the vessels of affected individuals are reminiscent of hypertensive arteriopathy with prominent degeneration and loss of vascular smooth muscle cells (VSMC). The etiological basis for this syndrome is mutations within one of the Notch family of genes, Notch3. These mutations are postulated to result in a functional loss of Notch3 signaling primarily affecting adult VSMC. Notch3 expression in normal adult tissue is largely confined to VSMC. However, the functional role and significance of Notch3 signaling in VSMC biology and arterial structure remains to be defined. Our preliminary studies have provided some initial insights into Notch3 signaling and function in VSMC. We have begun to define Notch3 as a mediator of VSMC growth and apoptosis. Furthermore, we have made the initial observation that Notch3 is expressed within the neointima after arterial injury. We postulate that Notch3 signaling is a critical determinant of VSMC fate and arterial structure by promoting growth and inhibiting apoptosis. However, the downstream effectors of Notch3 signaling in VSMC remain to be defined. The proposed project will test the central hypothesis that Notch3 signaling is a critical determinant of vascular remodeling and arterial structure by modulating downstream molecular cell fate determinants of VSMC growth and apoptosis through the sequential activation of an RBPJ- and HRT1-dependent transcriptional pathway. We propose to systematically implement both a loss- and gain-of-function strategy, to address two fundamental questions: 1) What are the downstream cell fate determinants modulated by Notch3 in VSMC and 2) What is the biological significance of Notch3 signaling as a functional and structural determinant in vitro and in vivo? Specifically, we will: Aim 1: Define the essential role of RBPJ-mediated activation of HRT1 as downstream effectors of a VSMC growth-stimulatory pathway induced by Notch3. Aim 2: Define the essential role of RBPJ-mediated activation of HRT1 as downstream effectors of a Notch3-induced VSMC survival pathway. Aim 3: Determine the functional role of Notch3 pathway activation on VSMC fate determination, vascular remodeling and lesion formation in vivo. Taken together, these findings will provide fundamental insight into transcriptional programs and molecular cell fate determinants of arteriopathic remodeling seen in hypertension and the genetic disorder, CADASIL.